Model Engine Maker
Engines => From Plans => Topic started by: Zephyrin on October 10, 2019, 10:18:59 PM
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Hi,
I’m planning to build a small gas engine, a 2-stroke engine this time, 1/2" bore and 1/2" stroke, 1.6 cm3, (0.097c.i.), with spark ignition. therefore a tiny engine, with a pleasant vintage style...
the plan comes from an old and unknown magazine that I’ve found here :
http://www.plans-for-everything.com/hen_ic_engine_plans.html
(http://www.plans-for-everything.com/hen_ic_engine_plans.html)
It is the “Parohl” engine whose link for the PDF is at the bottom of the page.
I don't know from which magazine this copy comes from, and the date, but it looks pretty old and the engine very appealing !
The author of the article says it is a (modified) plan by Henry Parohl.
A point that worries me is the transfer through a port in the skirt of the piston...as in the attached figure below.
Although this arrangement is often present on 2 strokes, I have never seen it on model glow or compression-ignition engines.
I fear that the gas flow during the transfer will be hindered around the connecting rod small end just in front of the piston port owing to the very small size of this engine.
What do you think of this plan and are there other model makers who have already made this engine?
Before cutting metal, I made new drawings with a few dimensions in metric units according to my tooling, and the corresponding angular diagram, and nothing unexpected in it.
I will start by casting a few parts in aluminium from patterns in boxwood I'm doing.
PS: I have just found that this copy comes from the magazine "Mechanics and Handicrafts", may 1937...
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Hi Zephyrin
I would be very surpriced if it runs poorly, but with that said - it will not be a performance engine either.
Oh and just to clarify - No modern high performance two-stroke, from 50cc to 500cc, has any "windows" in the piston (from the factory - aftermarked is a differen't story) - but I have seen a number off Car model racing engines still have them. I'm pretty sure that the reason the aftermarked still sell them with has everything to do with old dogs wanting what was "Top of the Pops" in their youth + haven't got a clue that two-strokes has evolved quite a bit since. If nothing else - that still applies to the Veteran Moped crowd here in Europe ....
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That's a very old design. I am writing a series on modern, high power glow ignition engines. The first articles in the series are:
namba.com/content/library/propwash/2018/october/14/ --History
namba.com/content/library/propwash/2019/april/24/ --Piston & Cylinder Fit
namba.com/content/library/propwash/2019/october/4/ --Head Design
Lohring Miller
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Thank you for the history lesson Lohring :ThumbsUp:
You did not post those as links, so I will try here :
http://namba.com/content/library/propwash/2018/october/14/ (http://namba.com/content/library/propwash/2018/october/14/)
namba.com/content/library/propwash/2019/april/24/ (http://namba.com/content/library/propwash/2019/april/24/)
namba.com/content/library/propwash/2019/october/4/ (http://namba.com/content/library/propwash/2019/october/4/)
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lots of exciting things in these pages, thanks Lohring...
I understand all that technics, flat piston top and Schnurle scavenging, multiported transfer etc.
But I'm not equipped to build competition engines, with brass chromed cylinder liner etc., therefore the old fashioned engine I'm doing has a deflector on the piston !
I rank myself rather in the category of veterans or old dogs mentioned above !
first metal parts yesterday, a few usable aluminium castings
I like to watch after casting the pieces out of the sand.
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Hi Zephyrin.
It's great to see the " Art " isn't quite dead! Some nice looking castings. :ThumbsUp:
If I may suggest? Your castings would have come out even better had you placed them in the " Drag " bottom box rather than the " Cope " top box.
You have the advantage of extra " head " pressure from the " Sprue " and any shrinkage will form in areas that won't be seen. ;)
Castings rule!!
Cheers Graham.
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Thanks for advices, Graham, being a beginner any suggestion is welcome !
If I understand correctly, I did the pour as in A in the figure, and I should have done it as in B ?
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Good morning Zephyrin.
Yes your patterns should be placed as in " B " but there's no need to run them from below.
The " pit " of the sprue in the drag is a good thing as it allows for hotter and cleaner metal to enter the mould cavity.
When moulding " loose " patterns, like you have, the " in gates/runners " can be cut from the sprue to the cavity either in the cope or the drag. The choice is determined by.... Needing to " fettle " the side of the casting if from the drag. Or not if the runner enters from above the cavity ( cope ) box.
Cheers Graham.
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Hi,
Thanks again Graham ! great forum with so much of shared expertise !
Crankshaft machining today, 2 crankshafts in fact as the first one was out of alignment, oh no! sh..
I did first as in the paper, entirely between centres: crankpin first, then the main journal, with a spacer between the webs of course, but it is difficult to estimate the flexibility between looseness and over tight centres.
I did the second with my usual way to do for small crankshaft, first the main journal between centre, both side to the finished size, then I machine the crankshaft blank in the three jaws, held in a specially made eccentric collet that holds the shaft off centre and the crankpin centered, thus, I eliminate the problem of the flexibility with so small diameters. One has to do a precise jig, but the result is flawless…as far as I can measure between such small web.
the shaft also should not be permitted to slip or turn in the jig...with a positive indexing as a pin or a milling for the web.
as I have the jig already made, I also did the crankshaft for the single bearing version, as it has the same throw, one never knows…
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Actually, I think a flat topped piston style engine is easier to build than a deflector piston design. You just need to get the transfer ports approximately right for moderate performance. A lapped cast iron piston in a steel sleeve also works well. Around 60 years ago I built an engine in high school shop. It was a state of the art deflector style engine for the time.
Lohring Miller
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Lohring
I have just read the article you have written on head design very interesting I will try some wider squish bands in one of my engines over the winter testing and development for my tether car engines
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This is a link to a really good book on model two stroke design.
Lohring Miller
http://controlline.org.uk/phpBB2/viewtopic.php?t=11848
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Thanks
I have a copy interesting read, I have seen some of his work its very nice Gordon is currently working on 1.5cc diesel engine with a cnc machined crankcase that he is producing himself.
My interest is high speed glow engines (Nitro) but no nitro just 80% methanol and 20% castor oil, my 2.5cc tether car engine runs around the 40,000 rpm range.
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Hi
Machining the aluminium casting is done, whew; not first class metal, which get soldered on tool and raises edges, making precision a chore!
I fear when I will have to tap hole in that junk...
The 2 half of the crankcase are not identical, one have a male and a female part.
I have removed a surprisingly large amount of swarf from so little castings, and the result is very very light.
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Thanks
I have a copy interesting read, I have seen some of his work its very nice Gordon is currently working on 1.5cc diesel engine with a cnc machined crankcase that he is producing himself.
My interest is high speed glow engines (Nitro) but no nitro just 80% methanol and 20% castor oil, my 2.5cc tether car engine runs around the 40,000 rpm range.
That's not a particularly high piston speed for a 2.5 cc engine. The connecting rod big end bearing starts to be the main issue as speeds go up. Jim Allen has done a lot of work on this in 15 cc engines turning in the 40,000 rpm area. My take on this is Big End Blues. (http://namba.com/content/library/propwash/2012/April/#/11/ ) I'm not sure that needle bearings have been tried in really small engines, but it would be interesting. Another issue is the rigidity of the crankcase and crankshaft bearings. I plan to address these mechanical issues in a future article.
Lohring Miller
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The 40,000 rpm figure is its racing rpm 165 mph, I have not run it under lighter load to see what the maximum rpm is. I don't want to break the engines. The Stelling 2.5cc engines are hard to find and no longer made but still very competitive. They have a steel front housing a heavy cast crank case compared to RC car engines and either drum or Zimmerman induction with a home made pipe.
I have run crowded needle roller big ends in tethered hydroplanes 10cc class they solve the problem of seized big ends, but so does increasing the clearance in the big end.
I also have a 10cc tether car engine with a crowded roller big end mine has never gone particularly fast, but the designers is the second fastest 10cc tether car in the world at around 214 mph, Msts has never told me what his engines rev to
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Interesting stuff :ThumbsUp: :ThumbsUp: I will be following along :wine1:
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The steel front ends should really help. It's easier to get good bearing fits when the coefficients of expansion are the same. Steel is also a lot stiffer than aluminum. The really fast tether cars should be at the cutting edge of glow engine development. I'm very interested in the details.
Lohring Miller
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HI,
I have installed the fixing screws between the two cranckase halves, pretty length job but no problem.
it seems to hold well, but it looks fragile, not much material on these legs for screw !
I hope that the tapping will resist upon several assemblies and disassemblies
Reaming (lapping in fact) of the bearings of the two assembled crankcase before the insertion of the bronze bushings to guarantee the concentricity and the proper alignment of both halves.
I have drilled and reamed the bronze bushings held in a collet in the lathe to the final dia (5) then on the same setting, turned their outside dimension, (exactly the same as the bore, 7.11) followed by 5 seconds with Norton microfinishing paper to remove tools marks and facilitate the sliding of the bushings into the aluminium castings.
I still had to force it a little bit with a bolt to get them in, without damaging my castings.
The crankshaft turns between the two crankase halves bolted together without any hard point, phew, not so easy...
I'm happy to have this part done...
https://photos.app.goo.gl/aPDpVnNWrMZHHvAK6
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Today; boring the crankcase for the cylinder, facing of its seating surface and adjusting its height. These tiny castings are hard to hold under the boring head.
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I turned the cylinder in a chunk of cast iron, which was lying around in my garage, not great as a metal.
No particular problem with the machining, but there is a small sealing profile in V on the top of the cylinder that corresponds with a female v on the cylinder head; I put it on, just for fun, because I think it's an unnecessary complication.
The 12 mm bore is then lapped to remove tool marks, up to a nice bore surface, and I get the small extra 0.01mm on the diameter at the bottom of the cylinder, as expected.
I got confused in the square base of the cylinder; I have to change the position and number of fixing screws, and to make sure that the screw holes do not open into the crankcase!
But at this point of completion, unfortunately, the cylinder fell to the ground, and a fin is broken, it's very ugly, alas.
On reflection, that lasted maybe longer than doing a new cylinder, I'll continue with this one, I'm anxious to see this engine running and I'll do another cylinder if everything goes well…
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What a shame :rant: after all that work and a nice result .....
I hope that the next is without incidents :cheers: :popcorn:
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Well, I didn't stay without doing anything…the engine is finished !
pictures of some more pieces!
The finished connecting rods, I had to re-bore a half-crankcase a little bit, to increase the diameter by 0.5mm, for the passage of the connecting rod !
I also had to reduce the size of the screws head, rubbing on the crankcase !
Everything turns well...phew
Machining the flywheel according to the plan, with the coned shape, not easy to measure its thickness ! I like the design of this flywheel I'll surely use it again one day !
The assembly is done by conical fitting on the crankshaft, tightened by a nut. So I turned the cone and thread between centre on the lathe, on a larger engine I prefer a coned bush.
The cylinder heads is also finished, with the V-groove that fits on the cylinder V, a nice part to turn and adjust. The thread for the plug is standard, 1/4" x 32; a bit big; some modellers make their own mini spark plugs, but I never tried it.
Piston is machined in a small cast iron bar, inside finished first, then the outside with 0.5 mm above the actual dia of the cylinder, then drilled for the wrist pin and milled for the port in the skirt and the deflector on the top. then the cylinder is put on mandrel in the lathe for turning the external face, up to the point where the piston start to go into the bottom of the cylinder; the final adjustment being made with a piece of Norton Q151 microfinishing film, pinched with the fingers between two steel rules on the piston in the lathe, for a series of about 5 seconds pass between testing the fit in the cylinder up to the “end” : i.e., the piston ( dry) enters fully in the cylinder with “some” resistance…hard to be more precise. At this point, the piston is ran in with oil by hand only in the cylinder for 5 min, then mounted in the engine for the test.
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Very nice :praise2: :praise2: Clearances in the crankcase are difficult to determine without sophisticated CAD. I make an approximation and then grind off the bits that cause problems ::)
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The cylinder is mounted on the crankcase, no paper gasket, just a thin coat of blue loctite.
The transfer cover is screwed with a dab of blue loctite too, the brazed steel carb base is screwed with a Klingerit gasket, to isolate the mixer from the heat of the cylinder.
The mixer is made from brass rod; a steel sewing needle, soft soldered, plugs a 0.35 mm dia fuel port when tightened!
The contact breaker is made of a piece of steel spiral spring with riveted silver contacts, far from ideal but I didn’t find tungsten ones small enough.
The cam is a steel cylinder held on the crankshaft by a cone and a screw, a flat is milled to give about 90° of dwell, and the corner rounded with a few file strokes.
I did two engines from this plan, with very little differences in the port design, just to see if there are perceptible changes in the running properties…
I had to make a new piston in the first one, owing to a poor compression, but I can’t wait to start the test as the second engine being ready to run.
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Here we are, the first running test !
This model started easily, with plain gasoline with 15% motor oil for the running in, and when hot, the motor start with a flip on the flywheel; I’m pretty happy with this !
I have the second engine to get it running ! not yet ready !
However the rpm are not regular, speed increases and decreases continuously, easily perceptible in the video: periodic faster puffs then slowing down.
Amongst possible causes, I first suspect sparks, which may diminish as rpm increases, or poor carburetion, with unstable richness of the fuel ?
https://www.youtube.com/watch?v=pSHh5WMR_Gk
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I do love the size and the sound. A very nice runner.
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Congratulations - you have a fine runner :cheers:
The hunting running and sound is not really different to all the European mopeds of my youth (the Japanese were much better), when they ran at low RPM's (idle or a bit above) without any load on them - they usually all cleared their throat when you opened the throttle and the engine pulled you forward (load).
The Japanese had much better carburetors, ignition (the whole electric system) and reed controlled inlet.
Two strokes can be very funny, when all is not perfect - especially the caburation .... :old:
Best wishes
Per
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I've made a new test yesterday, to continue running in...
sharper noise and blue smoke, speed is improved, and the engine reaches 5400 rpm under no load.
As the original plan refers to 3000 rpm, I suppose that this engine is finished at this point, higher idle speed would probably disintegrate some parts...
https://photos.app.goo.gl/Swcm75m6mpRP69sr6 (https://photos.app.goo.gl/Swcm75m6mpRP69sr6)
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Congratulations Zephyrin, a beautiful little motor running well.
Will it require some sort of cooling for a longer run? What sort of load are you planning to drive with it?
MJM460
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Thanks for the appreciations...
MJM460 :
This engine don't overheat, up to now, about 15 min of uninterrupted run, up to the end of the whole gas tank, 7-8 ml
he could run longer, but looking at an engine running unloaded is rapidly boring...and more noisy than watching paint drying.
so as soon as an engine run, I have to find something to drive...
truly, I don't know yet !
To change myself from live steam locos, I'm making plans for a gauge 1 little diesel shunting loco that I thought I would equip with a small 4 stroke of a similar size, 12mm bore & stroke, as space is scarce on such a model, but maybe I already have the engine !
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That's a nice runner :praise2: :praise2: unloaded two strokes seem somewhat unstable but settle down under load.
One of the members on here, Gail in NM, has made some gauge 1 IC locos:
https://www.youtube.com/watch?v=xXnWSJOSuE0
https://www.youtube.com/watch?v=a-csJ3As7dc
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i'm well aware of these great "diesel" shunter loco...this exactly the kind of model I'm planing to do...
about 2 years back I've emailed with Gail about this project, and he gave me very useful advices, a very helpful gentleman and a outstanding modeller!
for this project, I first thought of a small 4 st, "tiny -like" as suggested by Gail Graham, with a more realistic noise for a model of locomotive, but if this mini 2st is reliable, it could very well take its place!
I hope to be able to do this project during the year 2020, but the years pass so quickly ..
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I also finished the 2nd engine, made it a new cast iron piston, and both are now running “at their best” and easily reaches 5000 rpm without load, noise and fumes are there, everything is fine.
I give them small differences in the height of the port simply “to see “, but in fact I see no difference in the running…!
But I have only one contact breaker that works, yet identical : I simply grinded one spring, which seemed too strong, and the engine, being launched at speed with the dremel, refused to start, as sparks die as speed increases, whereas the contact breaker gives a nice spark turning the engine by hand. It took me a while to see the problem!!
video of the 2nd engine, which of course looks like the first one!
https://www.youtube.com/watch?v=BDey2ERMJT4
I clearly felt the ramp up with the advance of the ignition , not as clear on the video, (never easy to film during the action!) but the frequencies on the soundtrack confirm it ...
Maybe a power measurement, and tests with a propeller instead of the flywheel, but I consider this project as finished ...
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Runs even better than the first :)
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That's pretty cool!
Nice work.
Dave
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Awesome work.... :ThumbsUp:
:cheers:
Don
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thank you all for the appréciations and feedback...
Yes Jason, I also think the second one is better, but I'm not impartial, because it's my preferred !
In fact, these small engines seem to be unable to idle, they only know the maximum rpm, I guess it's due to their small size and power, and that limits their use a lot...
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As far as I can see your carburetor doesn't have any form of throttle. You will probably get a better rpm range with a throttle carb that by adjusting the ignition timing. I would hope for at least a 4-1 rev range. My 12cc twin will run from 2000 to 8000 rpm with a simple barrel carb.
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Yes, I put a simple mixing valve as drawn in the plan...
these old timer models are made to run at max rpm only, far from modern standard of today model engines, with full RC control, much more pleasant I agree.
I adjust the timing as speed increases, inducing further increase in rpm, up to an optimum, but at this setting the engine doesn't start easily !
I learned also that I can't get high speed without a quite stiff spring and a very small gap (less than 0.5mm) in the contact breaker.
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I can't stop making 2 stroke engine...
here is a third one, made using the tooling and some left-overs of the previous...As I also did lot of changes in the plan, I dare to call it a personal design !
This model runs well, at 4500 rpm unloaded, but refuses to start with a propeller.
https://www.youtube.com/watch?v=hJMx6hcSGGw
more pictures in this album:
https://photos.app.goo.gl/8wX7sXmDjmBYSYJF6
I learned a lot with these exercises, but the time has come to move on to other models...